Pemphigus vulgaris is a severe blistering disease characterized by a circulating IgG which binds to an unknown epidermal cell antigen and causes epidermal disadherance. The disease was uniformly fatal prior to the discovery that high dose corticosteroid therapy would induce a remission in most patients. However, steroid therapy has many well known complications, and a more specific therapy would be of great value. Pemphigus antigen is a cell surface glycoprotein which is expressed as early as 9 weeks gestational age on epidermal cells, on some epidermal carcinoma such as A431, and on human amnionic membranes. The size of pemphigus antigen is known to be 210 Kd by immunoprecipitation of epidermal cell extracts with pemphigus IgG but is reduced to 130 Kd and 80 Kd bands on SDS-polyacrylamide gel electrophoresis. Large scale purification of the antigen has not been accomplished to date using conventional methods. We propose to screen a human cDNA expression library made from human amnion and placenta messenger RNA using purified labeled pemphigus antibody as a probe. We hope thereby to identify bacterial clones which express pemphigus antigens in vitro. Analysis of such clones would enable us to derive the amino acid sequence for all or part of the pemphigus antigen, to isolate and study its gene(s) and to study the expression and regulation of this epidermal cell surface glycoprotein.